There are a variety of support columns that have two or more sections that are connected together by mating threads. One example of such a support column is U.S. Pat. No. 2,548,844 which issued to Meyers in 1951. The Meyers reference has a support element the upper end of which is externally threaded. The support element mates with an internally threaded extension sleeve to which is attached a centering plate. Relative rotation of the support element and the extension sleeve permits some telescopic adjustment of the length of the support column. A more recent example of such a support column is U.S. Pat. No. 5,588,264 which issued to Buzon in 1996. The Buzon reference includes a base member that is rotatably engaged with a support member. The base member includes a threaded cylindrical bore that engages a threaded cylindrical projection on the support member. Relative rotation of the base member and the support member permits some telescopic adjustment of the length of the support column.
Several potential dangers are associated with support columns that have two or more sections connected together by mating threads. One danger is that over rotation will result in the separation of the sections. Another danger is that there may be failure if there is insufficient telescopic engagement. In view of this danger, some jurisdictions have passed laws making it mandatory that some means be provided to prevent the separation of the sections and ensure adequate telescopic engagement.